1. Field of the Invention
The present invention relates to an exhaust gas sampling apparatus for analyzing contents in exhaust gas from an automobile, a motorboat, a mowing machine and so on.
2. Description of Related Art
The construction of an exhaust gas sampling apparatus according to the conventional art will be explained by referring to FIG. 8. In the figure, reference numeral 201 indicates an intake air supply conduit for supplying fresh air from outside, an end of which is enlarged in the diameter thereof so as to form an air intake 202, in which is provided a filter 203. To the intake air supply conduit 201 is connected an exhaust gas supply conduit 204, and a gas mixture circulation conduit 205 is formed downstream from the connecting portion of the intake air supply conduit 201 and the exhaust gas supply conduit 204, and through the gas mixture circulation conduit 205, exhaust gas diluted with fresh air is extracted to the downstream side by a blower 206 provided in the downstream side thereof.
Here, the reason for mixing the exhaust gas with fresh air from outside when analyzing the contents of the above-mentioned exhaust gas lies in that there is a necessity to lower a ratio of moisture within the exhaust gas by mixing with fresh air, since otherwise dew drops will be condensed due to a decrease in the temperature on the way, when trying to send a pure sample of exhaust gas to an analyzer.
Interrupting the gas mixture circulation conduit 205 in the down-stream side from the connecting portion of the above-mentioned intake air supply conduit 201 and exhaust gas supply conduit 204, there is provided a mixing device 207, and further provided is a venturi device 208 down-stream of the mixing device 207, for the purpose of maintaining the exhaust gas at a constant flow rate, as a means of conforming to the different displacements and exhaust flow rates of various kinds of engines.
Further, from the gas mixture circulation conduit 205 is divided a sampling conduit 209, in the downstream side from the above-mentioned mixing device 207 but up-stream from the above-mentioned venturi device 208, and this sampling conduit 209 is further divided into three (3) conduits, to each of which is connected one of sampling bags 211 . . . through one of joints 210 . . . , respectively.
Further, from the air supply conduit 201 leads a reference air supply conduit 220, from the flow up-stream from the connecting portion with the exhaust gas supply conduit 204, and this reference air supply conduit 220 is also divided into three (3) conduits to be connected to the sampling bags 211 . . . through one of the joints 210 . . . , respectively.
Furthermore, a lead back conduit 230 being connected to the analyzer is connected to or closed from each one of the divided conduits 209a and 220a by means of valves 230a . . . , while an exhaust conduit 240 is also connected to or closed from each one of the divided conduits 209a and 220a by means of valves 240a, respectively. Still, valves 212 and 222 are provided in the up-stream side from the valves 230a and 240a for each one of the divided conduits 209a and 220a, and also a reversible pump 241 is provided in the flow of the exhaust conduit 240.
The analyzing method in such an exhaust gas sampling apparatus according to the conventional art, the structure of which is mentioned in the above, will be described below, in particular with reference to the sampling conduit 209.
First, the pump is driven under the condition where the valves 212 are turned OPEN while the valves 230a and 240a are CLOSED, so as to introduce the diluted exhaust gas into each of the sampling bags 211 according to a measuring mode, and then the valves 212 and 240a are turned CLOSED while the valves 230a are OPEN, so as to send the diluted exhaust gas into the analyzer through the lead back conduit 230, thereby measuring carbon monoxide (CO), hydrocarbon (HC), nitrogen compounds (NOx) and so on in the exhaust gas, in accordance with the predetermined mode for measuring.
As such the measuring modes are already known as an LA-4 mode and a US06 mode, as per the regulations in the USA, for example. (There are also known a 10.15 mode and 11 mode, as per the domestic regulations in Japan.) Here, in accordance with the LA-4 mode, the contents in the exhaust gas are measured in each of the following time periods: (1) from starting of the engine up to a time point of a lapse of 504 sec., (2) from 505 seconds up to the time point of the lapse of 1,374 sec., and (3) from a re-starting after 10 minutes suspension of the engine up to the time point of the lapse of 504 sec. Accordingly, in the LA-4 mode, the exhaust gases during the above-mentioned intervals (1) to (3) must be collected into the sampling bags, respectively, and therefore there are prepared the three (3) pieces of the divided conduits and the three (3) bags.
Also, in accordance with the SU06 mode, in which the exhaust gas exhausted from the engine being at almost full throttle for ten (10) minutes is reserved or stored in the sampling bag to be analyzed, only one of the sampling bags is used according to this measuring mode.
In the case where the measurement of the above LA-4 mode is conducted with an ordinary gasoline engine, the flow rate is changed for each of the intervals (1) to (3) of the LA-4 mode, while suppressing the mixture with air to as low a ratio as possible, for obtaining correct measurement values. Therefore, because the gas mixture flowing within the gas mixture circulation conduit must be controlled to be from 3 to 9 m3/min in the flow rate thereof, the above-mentioned venturi, of a variable flow rate type, is utilized.
Further, in the US06 mode, the gas mixture must be controlled at 21 m3/min in the flow rate thereof.
FIG. 9(a) shows an enlarged cross sectional view taken along the direction of the flow in the venturi 208 of the variable flow rate type, and FIG. 9(b) shows an enlarged cross sectional view taken in the direction orthogonal to the direction of flow, wherein the cross sectional area of flow passage 252 at a neck portion 251 is changed by shifting an external wall or a core of the venturi in a relative manner, so as to control the flow rate through it.
When completing the measurement, the valves 212 and 230a are turned CLOSED while the valves 240a are OPEN, and air is sent into the sampling bags 211 by driving the reversible pump 241 of the exhaust conduit 240 into the reverse direction of rotation. Then, the reversible pump 241 is rotated in the forward direction to discharge the exhaust gas including the air within the sampling bag. The exhaust gas within the sampling bag is completely removed by repeating this operation, so as to be prepared for the next measurement.
In the exhaust gas sampling apparatus as mentioned above, an exhaust pipe of an automobile is connected to the exhaust gas supply conduit 204 and at the same time the blower 206 is driven, then the exhaust gas is diluted by mixing with the intake air, to a concentration wherein the mixture has a mass 20 times that of the exhaust gas constituent therein, so as to eliminate the condensation of water droplets due to the decrease in the temperature of the gas. After being sent through the sampling conduit 209, as well as the conduit divided therefrom, to be then stored in the bag 211, a portion of the exhaust gas is supplied to the analyzer to be analyzed.
However, when the exhaust gas exhausted from the engine is diluted to 20 times the mass thereof, it is difficult to obtain a correct result of the measurements. In particular, with an automobile of low pollution (emissions) installed with a lean bum gasoline engine which bums diluted fuel therein, the contents of the exhaust gas discharged from it is inherently near to those of the fresh air, and the drawback mentioned above is considerable.
Further, as the sampling conduit is used a conduit made from Teflon resin or that on which Teflon resin is coated, according to the conventional art. With this, however, pollution or soot is easily absorbed on the sampling conduit and also an ingredient of hydrocarbon is exuded from the Teflon resin, therefore it is unsuitable for use in the measurement of the emissions of an automobile of a low pollution type as discussed above.
Moreover, using sampling conduit 209 as an example, of the conventional art, when completing the predetermined sampling operations, the valves 230a are turned OPEN while keeping the valves 212 . . . in the CLOSED condition, and the reversible pump 241 is driven to rotate in the reverse direction so as to supply the air into the bags 211 . . . through the exhaust pipe 230, and thereafter, the reversible pump 241 is driven to rotate in the forward direction to discharge the gas from the bags. This is repeated several times so that no exhaust gas remains within the bags or the conduits connecting to the analyzer.
However, though conducting such air purging in the above-mentioned manner, the absolutely correct measurement value cannot be expected, since it is impossible to substitute the air for the exhaust gas remaining within the sampling conduit 209 at the side up-stream of the valves 212 . . . .
Furthermore, in the conventional art, the contents of the exhausts gas remaining within the conduits are removed by the air, however, since the contents contained in the exhaust gas are very small in quantity and are similar in composition to the fresh air, in particular in the case of the measurement for the low pollution car, no guarantee can be made of the correct measurement with such air purging.
Also, in the exhaust gas sampling apparatus of the conventional art, the analysis is made by connecting the sampling bags 211 to the conduits 209a . . . at the side of a main body thereof, therefore, the conduits must be elongated, which is troublesome in a case where the analyzer is located at a position far from the exhaust gas sampling apparatus. Further, on the passage thereof is generated the water condensation into which the contents of the exhaust gas dissolve, therefore, it is impossible to obtain a correct result of the analysis.
Even in the conventional apparatus, it is of course possible to divide the sampling bags 211 from the portion of the joints 210, however it is difficult to carry a large number of the bags, and there is a possibility of mistaking the bag in which the reference air is contained for the bag in which the diluted exhaust gas is contained to be measured.
Furthermore, even if it is possible to carry them, since the exhaust gas within the bags is cooled down during transport (flow) thereof through the conduits, causing water condensation, and into the condensation is dissolved the contents of the exhaust gas, it is therefore difficult to obtain the measurement correctly.
Also, the conventional apparatus includes a problem relating to the variable type of Venturi. In the conventional apparatus, for the purpose of decreasing the flow rate of the gas mixture, the core is shifted to the left-hand side in FIG. 9(a), so as to make the area of flow passage narrower. On the contrary, it is shifted to the right-hand side for increasing the flow rate, so as to widen the area of flow passage. For enabling both the measurement of the LA-4 mode and of the US06 mode, although it is theoretically adequate to set up the diameter size of the Venturi, in particular at the neck portion thereof, so that the flow rate of 21 m3/min can be obtained under the condition of fall opening thereof, it is difficult, however, to throttle correctly if the diameter at the neck portion is large, and the control of the flow rate in the vicinity of 3 m3/min comes to be difficult to achieve.
For this reason, in the case where the venturi of the variable flow rate type mentioned above is used, it is impossible to control the flow rate widely. Namely, the control of flow rate in the range from 3 to 21 m3/min is difficult to achieve by use of only one of the venturi of the variable flow rate type.
As a means for solving the above problem, by providing a plurality of Venturis of a fixed flow rate type, it is possible to achieve the control of flow rate by exchanging the OPEN and CLOSED states therebetween, however when doing so, it is difficult to change the flow rate continuously therewith. For controlling it finely, the number of the venturis of the fixed flow amount types must be increased, and the structure thereof thus becomes complicated.
Furthermore, when providing the plurality of venturis of the fixed flow amount types, the flow rate becomes unstable when they are exchanged therebetween.
According to the present invention, for solving the first problem (i.e., the problem of condensation of moisture), there is provided an exhaust gas sampling apparatus, comprising: an exhaust gas supply conduit; an intake air supply conduit; a gas mixture circulation conduit being formed by joining said exhaust gas supply conduit and said intake air supply conduit; and a sampling conduit, being divided from the passage of said gas mixture circulation conduit, wherein a gas mixture to be analyzed is extracted through said sampling conduits, and wherein said exhaust gas supply conduit, said intake air supply conduit, said gas mixture circulation conduit, said sampling conduit, or a portion thereof where the gas mixture is stored temporarily is provided with a heater for preventing condensation of moisture in the exhaust gas.
With such a construction, though being diluted up to 20 times by mass with fresh air according to the conventional art, the condensation of moisture can be prevented, and may be prevented even with the dilution of 5 times by mass, thereby improving the accuracy in the analysis thereof.
Also, it is possible to provide a heat exchanger on said sampling conduit, at the down-stream side from the portion where said sampling conduit is divided, for decreasing the temperature of the exhaust gas, so as to protect a blower from damage thereby.
Further, it is also possible to provide a heater in said intake air supply conduit, in the side up-stream from the portion being joined with said exhaust gas supply conduit. With such a construction, it is possible to effectively prevent the exhaust gas from being decreased in the temperature thereof.
Further, said sampling conduit may be provided in plural systems thereof, depending upon kinds of engines. With such a construction, the conduit, in which remain the exhaust gas and the constituents (i.e., soot or the like) of the exhaust gas from the ordinary engine can be avoided to be re-used for the analysis of the exhaust gas from an engine of a low pollution car, thereby enabling accurate measurement
Further, it is preferable to use the sampling conduit which is made from stainless steel. With the sampling conduit made from stainless steel, it is possible to prevent such drawbacks as the exuding of hydrocarbon from the conduit material, as occurs when heating the conduit made of Teflon, as well as providing for removal of any pollution or deposit therefrom easily, thereby increasing the accuracy in the measurement.
Furthermore, there is provided a lead back conduit, being connected between said sampling conduit and an analyzer, through which the exhaust gas to be analyzed flows, wherein said lead back conduit is able to introduce purging gas therein, thereby enabling increase in the accuracy of the measurement, compared to that of the conventional art. In particular, the purging gas is preferably nitrogen gas.
According to the present invention, for dissolving the second problem (i.e., the problem related to the sampling bags), there is provided an exhaust gas sampling apparatus for diluting exhaust gas with fresh air, storing the exhaust gas diluted into (a) sampling bag(s) once, and analyzing the stored diluted exhaust gas with an analyzer, comprising: a main body of a sampling apparatus; and a storage box, in which said sampling bags are positioned, being detachable from said main body of said sampling apparatus, wherein said storage box comprises: a connector unit for attaching and/or detaching the conduits on said main body of said sampling apparatus with the conduits within said storage box.
With such a construction, it is possible to move the large number of sampling bags at the same time, and also to connect the conduits with the analyzer with ease.
Also, it is preferable to provide a heater within said storage box. With provision of the heater, condensation of moisture within the exhaust gas to be analyzed can be prevented during the times of movement or waiting for analysis thereof.
Further, with provision of not only the heater but also of a temperature controller, it is possible to keep the temperature within the storage box constant, and further with installation of a battery within the storage box, it is also possible to keep the temperature within the storage box constant during the time of the moving.
Further, the above-mentioned connector unit can be constructed so that it holds a flexible conduit within said box in such a manner that it can be drawn out therefrom. With such a construction, a handling property thereof is improved.
Further, in the above-mentioned connector unit, it is also possible to form an opening(s) to blow out warm air held within said storage box to an outside thereof. With such a construction, it is possible to conduct the connection of conduits of the analyzer with the conduits drawn out from the box in warm atmosphere, so as to be free from condensation which would occur otherwise when connecting the conduits.
In particular, with provision of the connector unit being able to elevate up and down, it is possible to maintain the warm atmosphere in which the conduits are connected, so as to prevent occurrence of the condensation of moisture constituent in the exhaust gas.
According to the present invention, for solving the third problem (i.e., the problem related to the variable venturi), there is provided an exhaust gas sampling apparatus, comprising: an exhaust gas supply conduit; an intake air supply conduit; a gas mixture circulation conduit being formed by joining said exhaust gas supply conduit and said intake air supply conduit; a sampling conduit, being divided from said gas mixture circulation conduit and connecting to a passage thereof; and a venturi mechanism for controlling the flow rate of a gas mixture flowing within said gas mixture circulation conduit, wherein said venturi mechanism is constructed with a main venturi provided in line with said gas mixture circulation conduit, and a sub-venturi positioned in parallel with said main Venturi.
And, for example, in a case where said main venturi is a variable flow rate Venturi, and said sub-venturi a fixed flow rate venturi, the valve on the bypass passage is turned CLOSED in the LA-4 mode, while it is turned OPEN in the US06 mode, so as to conduct the sampling.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.